Doping-Induced Enhancement of Hydrogen Evolution at MoS2 Electrodes

TL;DR

This study uses theoretical calculations to show how doping MoS2 with Co, Ni, and Pt enhances hydrogen evolution efficiency by stabilizing key intermediates, with implications for designing better catalysts.

Contribution

It reveals the role of specific dopants in stabilizing hydrogen intermediates and modifies the understanding of active sites in MoS2 for HER.

Findings

Doping reduces overpotential for HER at edges.

Co doping maintains high activity at full edge substitution.

Ni and Pt doping deactivate the basal plane sites.

Abstract

Rate theory and DFT calculations of hydrogen evolution reaction (HER) on MoS2 with Co, Ni and Pt impurities show the significance of dihydrogen (H2*) complex where both hydrogen atoms are interacting with the surface. Stabilization of such a complex affects the competing Volmer-Heyrovsky (direct H2 release) and Volmer-Tafel (H2* intermediate) pathways. The resulting evolution proceeds with a very small overpotential for all dopants ($\eta$ = 0.1 to 0.2 V) at 25% edge substitution, significantly reduced from the already low $\eta$ = 0.27 V for the undoped edge. At full edge substitution, Co-MoS2 remains highly active ($\eta$ = 0.18 V) while Ni- and Pt-MoS2 are deactivated ($\eta$ = 0.4 to 0.5 V) due to unfavorable interaction with H2*. Instead of the single S-vacancy, the site of intrinsic activity in the basal plane was found to be the undercoordinated central Mo-atom in threefold S-vacancy configurations, enabling hydrogen evolution with $\eta$ = 0.52 V via a H2* intermediate. The impurity atoms interact favorably with the intrinsic sulfur vacancies on the basal plane, stabilizing but simultaneously deactivating the triple vacancy configuration. The calculated shifts in overpotential are consistent with reported measurements, and the dependence on doping level may explain variations in experimental observations.